The batteries of electrical accumulators, hereinafter denoted “batteries,” designed for storing an energy that is to be returned in electrical form, are characterized, in particular, by their storage capacities, in other words the total energy that they are capable of returning in the form of usable electrical currents and by their capability to deliver a maximum power in use. These two characteristics depend on the technologies used in the cells of the batteries and have consequences on the dimensions of the batteries and on their storage capacity per unit mass (J/g).
Thus, in practice, two main categories of batteries are associated with their uses: batteries designed for applications of the energy type, when the requirement is principally a high storage capacity for the battery, for example in order to provide the maximum autonomy to a system supplied by the battery, these batteries being sometimes denoted “batteries of the energy type;” and batteries designed for applications of the power type when the requirement is to deliver high powers in use, in particular in order to respond to high instantaneous power demands, for example for the power supply of power actuators driven by certain systems, these batteries being sometimes denoted “batteries of the power type.”
This distinction between “battery of the energy type” and “battery of the power type” is however artificial since all the types of batteries are characterized by their capacity for storing, and more particularly for returning, energy, and by their maximum current, and hence their maximum power delivered, and it therefore only corresponds to the extremes of a classification of the batteries depending on these two characteristics, which in practice prove to be antinomic.
Energy batteries supply a quantity of energy that is relatively large for a given mass but with discharge current intensities that are relatively low. Conversely, power batteries accept discharge current intensities that are relatively high for a given mass but, on the other hand, only supply a relatively small usable quantity of energy.
The Ragone diagram is known to those skilled in the art for illustrating the variation of the maximum mass power ratio of accumulators as a function of their mass storage capacity, for various cell technologies.
This diagram illustrates that, for a given cell technology, the capacity decreases as the maximum power increases.
A choice with regard to a model of batteries is therefore generally made according to the applications.
For example, in the field of vehicles with electric propulsion, the search for maneuverability and for high accelerations leads to the use of batteries of the “power” type and with capacities limited to the needs of the mission to be carried out so as to limit their mass.
On the contrary, the search for a significant autonomy or for a wide range of action leads to the use of batteries of the “energy” type and with limited maximum powers for the needs of the mission so as to also limit their mass.
In order to illustrate these aspects, in the case of an aircraft with electric propulsion, an aerobatics aircraft, demanding in terms of power but only needing a limited autonomy, will be equipped with batteries of the “power” type, whereas a touring aircraft, demanding in terms of autonomy but with no need for excessive power, will be equipped with batteries of the “energy” type.
Such a specialization is however detrimental when a device, in particular a vehicle, may be used in missions that are sometimes demanding in terms of power, and other times are demanding in terms of energy.